Upadhyayula V Varadaraju

HoErFe17-xGaxCy were synthesized by arc melting technique. The temperature dependence of the ac magnetic susceptibility (0.1 Oe; 313 Hz) was carried out in the temperature range 13 - 300 K using a SUMITOMO ac susceptometer. Based on the observations, a magnetic phase diagram was established.

The dependence of GMR properties on the magnetic (partially filled d-shell) and non-magnetic (closed d-shell) dopant elements in La0.7Ca0.3MnO3 and Pr0.7Ca0.3MnO3 has been studied. It is found that non-magnetic element substitution drastically affects the ferromagnetic transition temperature.

Praseodymium manganites doped with holmium Pr1-x-yHoxSryMnO3 (x=-0.1 in steps of 0.2 and y = 0.3, 0.5) have been prepared and characterized by powder X-ray diffraction, ac magnetic susceptibility, dc magnetic susceptibility, dc electrical resistivity (ρH=0 and ρH=1.2T) and electron microscopy studies. Both series have a pseudotetragonal distorted perovskite like structure (Pbnm space group). Magnetic and electrical properties of the manganites have been investigated and the compositions are ferromagnetic insulators which exhibit small values of negative magnetoresistance. The highest MR ratio (MR=(RO-RH)/RO) of 48% at 152 K for a field of 1.2T for Pr0.6Ho0.1Sr0.3MnO3. The results emphasize the role played by the dopant holmium. SEM studies show well structured grains which vary with concentration of the dopant. The compounds were found to favour antiferromagnetism with increasing x.